1. Field of the Invention
This invention relates to comminution apparatus and, more particularly, to a comminution apparatus and method for grinding a granular material such as a grain and is selectively adjustable to produce a product of a preselected particle size, the particle size ranging between a fine flour and a coarse particle.
2. The Prior Art
Throughout history, civilization has depended upon the harvest, storage and ultimate consumption of food grains such as corn, wheat, barley, rice, and the like. With minor exceptions, most grains are finely ground or otherwise reduced in particle size, ranging from a coarse meal to a fine flour, before being consumed either in its present state or incorporated into a food product. The grinding process alone consumes a considerable amount of time for the person responsible for this task. Historically, the fine grinding of a granular material such as a food grain was accomplished by engaging the grain between two grinding surfaces. The grinding surfaces are usually in the form of millstones or the like so that the fine grinding is done by the frictional engagement of the grain by relative movement of the grinding surfaces. This grinding process has evolved in time to produce on a commercial scale a very fine, uniform product. However, this type of grinding equipment is heavy, relatively expensive to manufacture and maintain and results in wear of the grinding surfaces with the worn material passing into the food product. Also, this particular grinding process contributes a substantial amount of heat to the flour product with a corresponding reduction in the nutritive value of the flour product.
One alternative device consists of a plurality of mating rows of perpendicular teeth on a stator and matching, corresponding rows of teeth mounted perpendicularly on a rotor. Grain is fed between the teeth and is thus ground or otherwise finely comminuted without much heating of the resulting product. The fineness of the resulting product is regulated by the rate of air flow with the grain introduced through the grain feed port. The result is poor control of the ratio of coarseness to fineness of the product. Furthermore, this device, because of its net production of an airflow, results in dust being dispensed into the atmosphere. Further, the device tends to be relatively noisy due to construction of the high speed motor used to drive the rotor as well as the exhaust air allowing the escape of noise from the apparatus.
Certain other prior art devices are known in the art and are disclosed in the following references:
Fritz (U.S. Pat. No. 1,634,026) discloses a feed cutter and grinder for grinding hay, grain, and the like. The grinder consists of a cylindrical housing with a plurality of holes 9 therethrough. A circumscribing band 10 with corresponding holes surrounds the housing and is adjustable to regulate the size of the openings 9. A plurality of cutter bars 25 are mounted on a shaft 24 (best seen in FIG. 1) and operate as beater bars to provide the grinding/cutting action.
Ellis (U.S. Pat. No. 2,641,971) discloses a paper stock pulper which operates as a blender-type apparatus inside a screen having three lobes (best seen in FIGS. 3 and 4) therein to redirect the paper stock back to the impellor. The description of this apparatus is best seen at column 3, lines 6-22.
Ward (U.S. Pat. No. 2,822,846) discloses a leaf grinder for grinding leaves for mulching and having a set of horizontally rotatable blades 47, 49, and 51 operating inside a cylindrical screen 35. The screen is of fixed size, as in the previous reference, and predetermines the size of particles to pass through the screen.
Heger (U.S. Pat. No. 3,386,670) discloses a grinding apparatus for milling of ceral grains wherein the comminuting blade rotates in a horizontal plane at a high speed and is surrounded by a sieve structure. The fineness of the meal obtained from this device is varied by providing the sieve structures interchangeably within the housing. Note also that the blade operates at the lower end of a feed column which, in turn, is surrounded by the screen structure.
It would, therefore, be a significant advancement in the art to provide a novel apparatus and method for comminuting a granular material to a predetermined degree of fineness in the absence of a net production of byproduct air and with a corresponding reduction in dust and noise. It would also be an advancement in the art to provide a novel comminution apparatus and method for comminuting a granular feed with a rotating cutter mechanism operating inside a screen enclosure wherein the size of the screen openings are selectively adjustable to readily produce a comminuted product having a predetermined size range. Such a novel apparatus and method is disclosed and claimed herein.